Basic Physics of the System
Bread rises (as you probably know) due to microorganisms, primarily yeast, converting sugars into CO₂ + byproducts. The CO₂ forms bubbles, stretching the gluten in the flour. In order for the bread to rise, the microorganisms must produce CO₂ faster than it can escape from the dough.
Graphed over time, the amount of CO₂ produced would start at 0, fairly quickly rise to its maximum (as the yeast, etc. come back from dormancy), then slowly decrease, eventually to 0 (as they run out of food and/or are overwhelmed by byproducts such as alcohol). The amount of gas escaping from the dough also changes over time. It must obviously start at 0, and probably increases over time (after all, there is more to escape), and eventually of course its all escaped and thus it must be 0 again, but I'm not sure of its exact shape. So, a diagram:
That's the basic physics of the system. At some point, the bread must fall. (Well, maybe in a 0-g environment it would shrink instead of fall, but…)
How the Environment Matters
The microorganisms are very sensitive to fairly small changes in their environment. In particular:
- Temperature. If your kitchen is 70°F and the author's is 80°F, it could easily take twice as long. The lower the temperature, the slow the microorganisms go (up to a point, once it gets too hot, they're not happy either).
- Hydration. If your bread dough is lower hydration (drier) than the author's, it'll be slowed down again. The recipe is written in volume measures (cups), as you know flour packs down. That leads to huge variations in how two different people measure it. Make sure to measure it how the author says to (hopefully it specified somewhere in the book). Scoop-and-sweep vs. sift-and-sweep can easily be 25% different. Preferably, spend $25 on a kitchen scale, and do your baking by weight.
- Salinity. Salt slows down yeast. If you happened to substitute table salt for kosher salt, and still measured out 1½ tablespoons, you've used more salt than the author wanted. A fair bit more.
- Age of your yeast. If your yeast is old (and sometimes the packets in the store have been sitting for ages), it may not have the same potency as a fresh packet would. It'll probably take longer (but as long as it rises, it'll likely be fine)
- The times in the book could just be nonsense. Authors and editors do sometimes make mistakes. Other times they're in a rush, and just take a guess. "Yeah, it was about two hours..." The book could just be wrong.
Also, generally speaking, slower leads to better flavor. So its not a bad thing.
Give it longer. Provided you've covered it in plastic (so it doesn't dry out), it'll eventually fall.
Keep in mind that "fall" doesn't mean it'll return to its original size, just that it'll fall back from its maximum size. The "or flattens on top" comment in your book is a pretty accurate description of what it looks like. Normally, while its rising, there is a dome shape on top, with the center as the highest point. When it starts falling, that dome vanishes, and may even invert (as in, the center will be the lowest point).
I've made preferments that take upwards of 20 hours to fall. It will eventually happen. And when it takes forever, it'll probably taste better.